A variety of equipment has been previously available for developing or desensitizing, i.e. fixing, photosensitive sheet material, but the prior equipment has not been entirely satisfactory. The term "developing" herein means to make visible a latent image or one that is barely visible, as in the diazo copying process. The term "desensitization" or "fixing" herein means to render a photosensitive copy sheet resistant to visible changes upon further exposure to light.
While the invention has broad utility, it is particularly useful in a process known as (1) "imposition or position proofing," i.e. proofing of graphic material to determine quickly how graphic material will appear when later printed on a printing press. Position proofing can be accomplished with either positive or negative (2) sensitized paper or laminated emulsions. In this process, an exposed sheet of transparent photographic film (one containing an image) is placed in contact with a sheet of the photosensitive copy paper that is to be later processed using the present invention. The superimposed sheets are then exposed to ultraviolet light to transfer the image from the film to the copy paper. The copy paper is, however, still sensitive to room light and, in order to be stabilized, must be fixed or desensitized. Desensitization is then accomplished by passing the copy sheet through the present invention. One example of photosensitive sheet material of this type is sold commercially by Fuji Photofilm USA, Inc. of Itasca, Ill., under the name Fuji Copyart.TM. CP3. Heat developable photosensitive sheet material is also described in a Japanese patent to Fuji, laid open #278849/1986. A further example is a positive Copyart.TM. Paper by Fuji Photofilm USA, Inc. Other heat developable or heat desensitizable photosensitive sheets that can be employed in connection with the invention are commercially available and are well known to those skilled in the art. In general, the present invention can be used for processing any paper or sensitized material that employs a thermal process to fix or desensitize graphic images for providing a broad tone range and clear color breaks allowing the printer to achieve more clear and accurate proofing prior to a monochromatic or multicolor press run.
In these prior applications, a number of deficiencies have been experienced. In the past, difficulties have been encountered in achieving uniformity when treating large sheets, e.g. sheets measuring 36 inches or more in width. Desensitization was sometimes inconsistent from one portion of the copy sheet to another. Maintaining consistent results over a period of time, e.g. from the beginning of a run to the end of the run has also been difficult to accomplish in the past.
It is therefore a general objective of the invention to provide an apparatus for developing or desensitizing photosensitive sheet material in which the degree of development or desensitization is consistent over time and from one portion of the copy of sheet to another.
A more specific object is to effect treatment of photosensitive copy sheets by the application of heat with a temperature variation no greater than about +5.degree. F. and most preferably no greater than about of +2.5.degree. F.
Another object is to prevent undesirable temperature variations that have occurred in the past across the width of the sheet, i.e. in the cross-machine direction.
A further object is to provide an apparatus of the type described that is rugged in construction, low in cost, and reliable in applying heat uniformly to all portions of the sheet material being processed.
Another object is to provide cabinetry that will prevent the operator from accidentally coming into contact with the heater or other portions of the machine that could burn the skin or is hot to the touch, or could overheat components, e.g. electronic controls or drive motor.
A further object is to prevent damage to the photosensitive sheet material caused by moisture that is liberated during treatment.
Still another object is to isolate the heating element from the mechanical components and drive train for long life and operation.
Yet another object is to reduce processing time by employing relatively a high processing temperatures but without deleterious effects previously caused by overheating.
These and other more detailed and specific objects of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.